1. Field of the Invention
The present invention relates to an oscillation type angular velocity measuring device and, more particularly, to an angular velocity measuring device capable of reducing the influence of the oscillation of an oscillator in an oscillating direction.
2. Description of the Related Art
A mechanical quantity measuring device mentioned in JP-A 2002-188923 is an example of an angular velocity measuring device provided with two oscillators placed on a substrate, such as a silicon substrate, and a connecting beam elastically connecting the two oscillators.
Reduction of the influence of oscillation is a problem in the oscillation type angular velocity measuring device.
The foregoing known angular velocity measuring device provides in-phase signals indicating variations of the respective capacitances of flat electrodes attached to two oscillators related with an oscillation along an X-axis extending in the direction of oscillation of the oscillators and an oscillation along a Y-axis extending in a direction perpendicular to the direction of oscillation and parallel to the substrate. As regards angular velocity, it is intended to eliminate the influence of oscillation, which is an in-phase component, by determining the difference between the two oscillators by using a differential signal.
However, the foregoing prior art does not take anything into consideration about the very sharp reaction of the two oscillators to oscillations along the X-axis.
In the oscillation type angular velocity measuring device, viscous force (damping effect) acting in directions parallel to the X-axis is diminished and Q (an index of ability with resonance) is increased so that oscillators oscillate in a large amplitude in directions parallel to the X-axis to enhance the sensitivity to angular velocity. The structure formed by elastically connecting the two oscillators by the connecting beam has two oscillation modes, namely, a differential oscillation mode and an in-phase oscillation mode. Since an oscillation in the differential oscillation mode affects angular velocity measuring sensitivity, a high Q is desired. Since an oscillation in the in-phase oscillation mode cause an error in angular velocity measurement, a low Q is desired. When the viscous force acting in directions parallel to the X-axis is reduced and the Q of the differential oscillation is increased, the Q of the in-phase oscillation increases.
In the angular velocity measuring device provided with the two oscillators connected by the elastic connecting beam, the resonance frequency of an in-phase oscillation is lower than that of the differential oscillation. The resonance frequency of the in-phase oscillation is dependent on the spring constant of a support beam elastically supporting the two oscillators and the substrate. The stress influence of the substrate can be reduced when support beam has a low spring constant. However, when the support beam has a low spring constant, the resonance frequency of the in-phase oscillation is low and the strength of the oscillation parallel to the X-axis acting on the angular velocity measuring device is reduced; that is, when the two oscillators make an in-phase oscillation of a resonance frequency, the two oscillators making the in-phase oscillation resonate to cause a large error in a measured angular velocity. Although oscillations that act on the angular velocity measuring device can be reduced by a known method that uses an oscillation absorbing member, such as a rubber member, the lower the frequency of the oscillation, the lower is the oscillation reducing effect of the oscillation absorbing member.
In other words, in the angular velocity measuring device provided with the two oscillators connected by the elastic connecting beam, the Q of the in-phase oscillation increases when the Q of the differential oscillation is increased by reducing the viscous force (damping effect) acting in a direction parallel to the X-axis, and the resonance frequency of the in-phase oscillation decreases and the influence of oscillation becomes worse when an support beam having a low spring constant is used to reduce the stress influence of the substrate.